EELS measurements of boron concentration profiles in p-a-Si and nip a-Si solar cells

Bas B. Van Aken, Martial Duchamp, Chris Boothroyd, Rafal E. Dunin-Borkowski, Keiji Tanaka, H. Hosono, Hiroyuki Fujiwara, Seiichiro Higashi Seiichi Miyazaki

    Research output: Contribution to journalConference articleResearchpeer-review

    Abstract

    The p-type Si layer in a-Si and μc-Si solar cells on foil needs to fulfil several important requirements. The layer is necessary to create the electric field that separates the photo-generated charge carriers; the doping also increases the conductivity to conduct the photocurrent to the front contact; on the other hand, the p-layer should transmit the incident light efficiently to the intrinsic absorber layer. We show that it is possible to study TEM samples prepared, for analysis of possible layer defects, by focussed ion beam milling to detect boron and carbon concentrations as low as 1020cm-3, using core-loss EELS combined with numerical analysis. We control the band gap and activation energy of p-a-SiC by varying the B2H6 and CH4 flow during deposition in the process chamber. We have found a linear relation between the activation energy of the dark conductivity Eact and the optical band gap E04. Modelling shows that the optimum efficiency in nip solar cells is obtained when the p-a-SiC band gap is slightly larger than the band gap of the absorber layer. We have assessed the potential of core-loss EELS for detecting B and C concentrations as low as 1020cm-3 in a spatially resolved manner, and of low-loss EELS as a probe of the local variations in plasmon energy.
    Original languageEnglish
    JournalJournal of Non-Crystalline Solids
    Volume358
    Issue number17
    Pages (from-to)2179-2182
    ISSN0022-3093
    DOIs
    Publication statusPublished - 2012
    Event24th International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 2011) - Nara, Japan
    Duration: 21 Aug 201126 Aug 2011

    Conference

    Conference24th International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS 2011)
    CountryJapan
    CityNara
    Period21/08/201126/08/2011

    Keywords

    • Electron energy loss spectroscopy (EELS)
    • Thin film Si
    • Transmission electron microscopy
    • p-Type SiC
    • Doping concentration

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